Identification of Lithiation Mechanisms in Silicon-Carbon Multilayer Electrodes for Li-Ion Batteries Using Operando Neutron Reflectometry

Operando neutron reflectometry was used to investigate the redistribution of Li during electrochemical insertion into and extraction from stratified amorphous silicon/carbon (Si/C) multilayer electrodes for lithium-ion batteries (lithiation mechanism). Constant-current cycling from low to high rates (4–160 μA cm−2, C/40−2C) was applied during reflectometry measurements. Due to the multilayer structure, Bragg peaks are detected in the reflectivity pattern. By analyzing changes in both the intensity and the scattering vector positions of these peaks during electrochemical cycling, specific lithiation and delithiation mechanisms were identified. During initial lithiation, a heterogeneous, moving phase-front mechanism dominates, followed by a superimposed homogeneous mechanism. In contrast, delithiation and subsequent cycles are primarily governed by a homogeneous mechanism. Additionally, the lithium content of the lithiated phase is influenced by both the silicon-layer thickness and the lithiation rate.